If you knew lactic acid burns fat, how would your workouts change? And to what end? The American Council on Exercise defines lactic acid production as a physical state following the first few minutes of vigorous exercise, where blood fails to transport enough oxygen into working muscles to meet activity demands. In this anaerobic state, you may feel winded and your muscles will more than likely ache or burn.
Lactic Burning Threshold
With most ergometric exercise, you readily shift into an aerobic state that uses energy with oxygen, often referred to as "getting your second wind." This enables you to maintain a certain threshold of activity for an extended duration without constant pain. Fat-burning hormones cortisol, epinephrine and adensosine triphosphate, or ATP, release at a perpetual rate after 20 to 40 minutes. Weightlifting, on the other hand, pushes you to lactic-burning threshold upon maintaining muscle contraction beyond 20 seconds. The ability to perform repetitions in a constant state of lactic acid release is far more likely to occur on a treadmill than a bench press.
Muscle Cell Rebound
Some fitness experts argue that training at lactic acid threshold is necessary to burn fat, citing an Australian study published in 2004. Researchers determined lactic acid wasn't a chief factor in muscle fatigue, but played a role instead in assisting muscles to contract more efficiently. The study demonstrated that potassium ions reenter cell membranes after lactic acid removes accumulated chloride, making it easier for muscles to work. They also observed that lactic acid did not make muscles more acidic.
Drawing Overextended Conclusions
A similar study conducted at the Cooper Institute Centers for Integrated Health Research found that enterically coated oral ATP supplements ingested before exercise made small but measurable benefits on athletic performance in certain trials. This led some trainers to draw overextended conclusions about the benefits of training in lactic acid threshold; that workouts using high-volume weight training, interval training, or circuit training promote fat burning because of lactic acid production, and that its presence remains locked in the muscles for hours following workout. The problem: Once you stop anaerobic activity and respiration returns to normal, your cells eliminate lactic acid within one to two minutes.
Short-Term Safety and Long-Term Conditioning
Both studies indicate your body can teach itself to benefit from lactic acid, and its production is counterpart to creating the muscles' ability to withstand more work. The tendency to produce lactic acid during vigorous exercise therefore serves chiefly as a conditioning component. It enables you to increase muscle strength and endurance long term, prevents you from overdoing short term, but remains an inefficient mechanism for burning fat.